diff --git a/src/Lean/Util/FindExpr.lean b/src/Lean/Util/FindExpr.lean
index a93765a3cb8c..e9788ea76bf1 100644
--- a/src/Lean/Util/FindExpr.lean
+++ b/src/Lean/Util/FindExpr.lean
@@ -11,17 +11,17 @@ namespace Lean
 namespace Expr
 namespace FindImpl
 
-unsafe abbrev FindM := StateT (PtrSet Expr) Id
+unsafe abbrev FindM (m) := StateT (PtrSet Expr) m
 
-@[inline] unsafe def checkVisited (e : Expr) : OptionT FindM Unit := do
+@[inline] unsafe def checkVisited [Monad m] (e : Expr) : OptionT (FindM m) Unit := do
   if (← get).contains e then
     failure
   modify fun s => s.insert e
 
-unsafe def findM? (p : Expr → Bool) (e : Expr) : OptionT FindM Expr :=
+unsafe def findM? [Monad m] (p : Expr → m Bool) (e : Expr) : OptionT (FindM m) Expr :=
   let rec visit (e : Expr) := do
     checkVisited e
-    if p e then
+    if ← p e then
       pure e
     else match e with
       | .forallE _ d b _ => visit d <|> visit b
@@ -33,29 +33,35 @@ unsafe def findM? (p : Expr → Bool) (e : Expr) : OptionT FindM Expr :=
       | _                => failure
   visit e
 
-unsafe def findUnsafe? (p : Expr → Bool) (e : Expr) : Option Expr :=
-  Id.run <| findM? p e |>.run' mkPtrSet
+unsafe def findUnsafeM? {m} [Monad m] (p : Expr → m Bool) (e : Expr) : m (Option Expr) :=
+  findM? p e |>.run' mkPtrSet
+
+@[inline] unsafe def findUnsafe? (p : Expr → Bool) (e : Expr) : Option Expr := findUnsafeM? (m := Id) p e
 
 end FindImpl
 
-@[implemented_by FindImpl.findUnsafe?]
-def find? (p : Expr → Bool) (e : Expr) : Option Expr :=
-  /- This is a reference implementation for the unsafe one above -/
-  if p e then
-    some e
+@[implemented_by FindImpl.findUnsafeM?]
+/- This is a reference implementation for the unsafe one above -/
+def findM? [Monad m] (p : Expr → m Bool) (e : Expr) : m (Option Expr) := do
+  if ← p e then
+    return some e
   else match e with
-    | .forallE _ d b _ => find? p d <|> find? p b
-    | .lam _ d b _     => find? p d <|> find? p b
-    | .mdata _ b       => find? p b
-    | .letE _ t v b _  => find? p t <|> find? p v <|> find? p b
-    | .app f a         => find? p f <|> find? p a
-    | .proj _ _ b      => find? p b
-    | _                => none
+    | .forallE _ d b _ => findM? p d <||> findM? p b
+    | .lam _ d b _     => findM? p d <||> findM? p b
+    | .mdata _ b       => findM? p b
+    | .letE _ t v b _  => findM? p t <||> findM? p v <||> findM? p b
+    | .app f a         => findM? p f <||> findM? p a
+    | .proj _ _ b      => findM? p b
+    | _                => pure none
+
+@[implemented_by FindImpl.findUnsafe?]
+def find? (p : Expr → Bool) (e : Expr) : Option Expr := findM? (m := Id) p e
 
 /-- Return true if `e` occurs in `t` -/
 def occurs (e : Expr) (t : Expr) : Bool :=
   (t.find? fun s => s == e).isSome
 
+
 /--
   Return type for `findExt?` function argument.
 -/
@@ -66,7 +72,7 @@ inductive FindStep where
 
 namespace FindExtImpl
 
-unsafe def findM? (p : Expr → FindStep) (e : Expr) : OptionT FindImpl.FindM Expr :=
+unsafe def findM? (p : Expr → FindStep) (e : Expr) : OptionT (FindImpl.FindM Id) Expr :=
   visit e
 where
   visitApp (e : Expr) :=